The present invention relates to a flame-retardant resin composition and more particularly to a resin composition which is excellent in flame retardance and further in heat resistance. Thus, moldings obtained using the resin composition of the present invention are useful as home electric appliances, electronic parts, car parts, construction materials and so forth.
Styrene-based resins are widely used in a wide variety of applications, for example, as home electric appliances, construction materials and further as interior materials because of their excellent properties.
The styrene-based resins, however, are easily combustible and their moldings once started to burn continue to burn even if the flame is removed. Because of this disadvantage, the styrene-based resins can be used only in limited applications.
While polystyrenes already on market, that is, atactic polystyrenes, and polycarbonate resin and ABS resin are non-crystalline, the styrene-based polymer having mainly syndiotactic configuration used in the present invention is crystalline.
As flame retardants to be compounded with the styrene-based polymer having mainly syndiotactic configuration, accordingly, those which might hinder the heat resistance attributed to crystallization as the feature of the styrene-based polymer having mainly syndiotactic configuration (abbreviated as SPS), in other words, those which might lower the Distortion-Temperature under Heat (H.D.T.) of SPS composition are not proper.
SPS compositions are used at high temperatures, making the best use of the heat resistance attributed to crystallization that is one of the characteristic features of SPS.
To compound a flame retardant with SPS, it is required to select a flame retardant that has not only flame retardance but also is free from bleeding out, discoloration of moldings or lowering in mechanical properties in any circumstances, and to determine the amount compounded. Consequently, in this respect it has been insufficient to merely select as flame retardant a compound which is high in melting point and decomposition temperature.
As a result of further investigations to overcome the above problems, specifically using a styrene-based polymer having mainly syndiotactic configuration which was developed by employee of the present assignee (see Japanese Patent Application Laid-Open No. 104818/1987), it has been found that a resin composition having the desired physical properties can be obtained by adding specified amounts of a specified flame retardant and auxiliary flame retardant to a styrene-based polymer having mainly syndiotactic configuration or a mixture of the styrene-based resin and a thermoplastic resin and/or rubber and, in particular, a resin composition containing a specified flame-retardant and an auxiliary flame retardant, polytetrafluoroethylene, in a specified ratio is effective in preventing melt dropping which is responsible for the spreading of fire of the resin composition.